Three-Dimensional Structure and Dust Extinction in the Small Magellanic Cloud

TL;DR

This study models the 3D structure and dust extinction in a region of the Small Magellanic Cloud using Hubble data, revealing a large line-of-sight extent and dust distribution offset from stars.

Contribution

It provides the first joint analysis of dust extinction and 3D geometry in a specific SMC region using CMD modeling, demonstrating a new approach.

Findings

The SMC region has a line-of-sight extent of about 11.3 kpc.

Dust is offset on the near side by approximately 3.2 kpc.

The mean extinction A_V is 0.41 mag, with a dust-to-gas ratio lower than the Milky Way.

Abstract

We examine the three-dimensional structure and dust extinction properties in a ~ 200 pc $\times$ 100 pc region in the southwest bar of the Small Magellanic Cloud (SMC). We model a deep Hubble Space Telescope optical color-magnitude diagram (CMD) of red clump and red giant branch stars to infer the dust extinction and galactic structure. We model the distance distribution of the stellar component with a Gaussian and find a centroid distance of 65.2 kpc (distance modulus $\mu$ = 19.07 mag) with a FWHM $\approx$ 11.3 kpc. This large extent along the line of sight reproduces results from previous studies using variable stars and red clump stars. Additionally, we find an offset between the stellar and dust distributions, with the dust on the near side relative to the stars by 3.22 $^{+1.69}_{-1.44}$ kpc, resulting in a 73% reddened fraction of stars. Modeling the dust layer with a log-normal $A_V$ distribution indicates a mean extinction $\langle A_V \rangle$ = 0.41 $\pm$ 0.09 mag. We also calculate $A_V/N_H$ = 3.2 - 4.2 $\times10^{-23}$ mag cm$^2$ H$^{-1}$ which is significantly lower than the Milky Way value but is comparable to previous SMC dust-to-gas ratio measurements. Our results yield the first joint dust extinction and 3D geometry properties in a key region in the SMC. This study demonstrates that CMD modeling can be a powerful tool to simultaneously constrain dust extinction and geometry properties in nearby galaxies.